US Commerce Secretary John Bryson has taken medical leave, after he was found unconscious following two mysterious hit-and-run car accidents, possibly caused by a seizure, the White House said.

Bryson, 68, is under investigation over two incidents in Californiaon Saturday, where he was traveling privately without his security detail. Authorities say neither alcohol nor drugs are suspected.

President Barack Obama's spokesman Jay Carney said Bryson told the White House Monday night that he would take a medical leave pending "tests and evaluations" but did not say how long he would be absent.

Earlier, Obama had told an Iowa television station that he hoped that Bryson was well, and that he was seeking clarity on exactly what happened.

"We are still trying to find out, it sounds like it was health-related in some way, but we are going to make sure that obviously he gets the best care and we will be able to make a determination from there," Obama said.

Carney said Bryson, who is back in Washington, assured the White House "that the Commerce Department staff will not miss a beat in their work helping America's businesses compete."

A statement from the Los Angeles County Sheriff's Department said Bryson's Lexus rear-ended another car Saturday as it waited at a railway crossing in the city of San Gabriel.

According to the statement, Bryson spoke with three men in the damaged car and then drove away, hitting their Buick again in the process.

He then drove to the city of Rosemead, where he struck a second car, said officials, who said the secretary later was found "alone and unconscious behind the wheel of his vehicle."

Bryson was treated at the scene by paramedics, and then transported to a local hospital where he received "treatment for non life-threatening injuries," the sheriff's department said.

CNN reported that Bryson had no previous history of seizures, while the LA Times cited sources saying he had "limited recall" about Saturday's events.

News reports earlier Monday had said that Bryson was under investigation for the charge of felony hit-and-run, but it is unclear whether charges will be pressed if the collisions were found to be due to a medical condition.

"The preliminary investigation at the scene showed no indication of alcohol or drugs," said LA County Sheriff's Department spokesman Mike Parker, while officials noted that the crashes resulted in only minor injuries to others.

The Commerce Department said an investigation had been launched, adding that Bryson had no public events scheduled for Monday.

A Commerce official who spoke on background said that at the time of the accidents, Bryson was "on personal time with no security detail," since he was not on official business.

"He was driving his own vehicle. He was given medication to treat the seizure," the official said.

Bryson, who has a home in the area, was in southern California to give the commencement address at Pasadena Polytechnic School on Thursday, which his four daughters once attended, according to school officials cited by the LA Times.

Carney said Obama had not spoken to Bryson since the incident, but that his chief of staff Jack Lew had done so.

Bryson was confirmed as commerce secretary in October of last year, replacing Gary Locke who was named US ambassador to China.

Prior to taking up his post at the department, he was chairman, chief executive and president of Edison International, the parent company of Southern California Edison.